Type II heterojunction in hierarchically porous zinc oxide/graphitic carbon nitride microspheres promoting photocatalytic activity

Graphitic carbon nitride (g-C₃N₄) is a visible light active semiconductor. However, low conductivity and high recombination rate of photogenerated electrons and holes limit its application in photocatalysis. In this work, we design and synthesize hierarchically porous zinc oxide/graphitic carbon nitride (ZnO/g-C₃N₄) microspheres with type-II heterojunction to effectively degrade rhodamine B (RhB) via increasing the charge-separation efficiency. The ultraviolet-visible (UV–Vis) absorption spectra, Mott-Schottky plots and valence band X-ray photoelectron spectroscope confirm the formation of type-II heterojunction between ZnO nanocrystals and g-C₃N₄ nanosheets. As a result, the 1.5-ZnO/g-C₃N₄ composite (the mass ratio of zinc acetate dihydrate to g-C₃N₄ is 1.5) exhibits the highest photocatalytic activity with good stability and higher photocatalytic degradation rate comparing to pure g-C₃N₄ and pure ZnO. In addition, our results confirm that ^[rad]O₂ ⁻ and h⁺ are the main active species for ZnO/g-C₃N₄ in degradation of RhB.